Garage door opener systems typically consist of large motor units containing various circuits and components. With this complexity there is a degree of difficulty in assembly requiring a great deal of time and a skilled assembler. In addition, this complexity is often due to the use of larger, less expensive and more reliable electric motors. Such motors, because of their higher operating speeds, must be stepped down in some manner to a safe operating speed. The mechanisms by which such speed reduction is accomplished is both a disadvantage economically and in mechanic reliability because of the higher incidence of malfunctions as the number of components increases. Further, such mechanisms represent a decrease in security, since such indirect linkages have lower resistance and can be forced more easily than direct linkages.
The speed at which a garage door opener mechanism raises or lowers the garage door is of major concern. A garage door can weight as much as seven hundred pounds, and can easily injure a foot or fingers which are left in the way. Several years ago Underwriters Laboratory required that safety circuits be incorporated which would reverse the movement of garage doors if an obstruction is encountered. Still, such circuits may be absent on older mechanisms, or may cease to function because of use and whether injuries continue to occur, particularly with young children trying to beat the door.